Trigger points or trigger sites are hyper irritable spots in skeletal muscle that are linked to palpable nodules in taut bands of muscle fibers. Trigger point practitioners hold that palpable nodules are small contraction knots which in that is a common cause of pain. When a trigger point is compressed, it may elicit local tenderness, referred pain, or a local twitch response.

Know the difference between a local twitch response and a muscle spasm

The local twitch response is different from a muscle spasm. This is because a muscle spasm refers to the entire muscle completely contracting, whereas the local twitch response also refers to the entire muscle but only includes a small twitch, and no contraction. The trigger point model explains that unexplained pain often radiates from these points of local tenderness to broad areas, sometimes far away from the trigger point itself.